After a nearly 20-year upward trend, U.S. CO2 emissions from energy took a sharp and unexpected turn downwards in 2007. By 2013, the country’s annual CO2 emissions had decreased by 11% – a decline not witnessed since the 1979 oil crisis.

Experts have generally attributed this decrease to the economic recession, and to a huge surge in cheap natural gas displacing coal in the U.S. energy mix. But those same experts mostly overlooked another key factor: the parallel rise in renewable energy production from sources like wind and solar, which expanded substantially over the same 2007-2013 timeframe.

Between 2007 and 2013, wind generated electricity grew almost five-fold to 168 TWh and utility-scale solar from 0.6 TWh to 8.7 TWh. During the same period, bioenergy production grew 39 percent to 4,800 trillion BTUs.

Decomposition analysis is an established method which enables us to separate different factors of influence on total CO2-emissions and identify the contribution of each to the observed decrease. The factors considered here are total energy demand, the share of gas in the fossil fuel mix (capturing the switch from coal and petroleum to gas), and the share of renewables and nuclear energy in total energy production.

Introducing a new approach for separately quantifying the contributions from renewables, we find that renewables played a crucial role in driving U.S. energy CO­2 emissions down between 2007 and 2013 – something which has previously largely gone unrecognized.

According to our index decomposition analysis, of the total 640 million metric ton (Mt) decrease (11%) during that period two-thirds resulted from changes in the composition of the U.S. energy mix (with the remaining third due to a reduction in primary energy demand). Of that, renewables contributed roughly 200 Mt reductions, about a third of the total drop in energy CO2 emissions. That’s about the same as the contribution of the coal and petroleum-to-gas switch (215 Mt). Conversely, increases in nuclear generation contributed a relatively minor 35 Mt.

While the significant role of renewables in reducing CO2 emissions does not diminish the contribution of the switch to natural gas, it is important to note that the climate benefits of switching from coal and petroleum to gas are undermined by the presence of methane leakage along the natural gas supply chain, the extent of which is likely underestimated in national greenhouse gas (GHG) emissions inventories.

Methane, of course, is a powerful greenhouse gas. Methane leakage from increased natural gas use could have wiped out up to 30% of the short-term GHG benefit (on a CO2-equivalent basis) calculated in this paper of switching from coal and petroleum to natural gas. For the natural gas industry to truly sustain the claim that it has made a positive contribution to reducing the country’s carbon footprint, the methane emissions associated with natural gas must be substantially reduced.

These results show that past incentives to support the expansion of renewable energy have been successful in reducing the country’s emissions, and that decreasing costs for renewable energy offers some hope for continued progress even despite the current administration’s refusal to address climate change.

Such progress, however, will never be sufficient without ambitious climate and clean energy policies- whether at the federal or at the state level – that can drive further emission reductions.

And then there were three. As of January 1st, 2018, Ontario has joined California and Québec, linking their respective carbon markets. In a post-Paris world of bottom-up climate policy, linking of climate policy matters. It provides a concrete step forward on the Paris Declaration on Carbon Pricing in the Americas. It shows that, while the U.S. federal government is dismantling much-needed climate protections, states, together with Canadian provinces, are moving forward. Linking, if done right, can be a powerful enabler of greater ambition. It also raises important questions.

To be clear, there are real advantages to linking carbon markets: Linking of climate policies is a political affirmation of joint goals and a signal to others to move toward concerted carbon policies. It also shows the real advantages of market-based environmental policies. Bigger markets also afford greater cost-savings opportunities.

The textbook illustration of such savings is instructive. Take two jurisdictions, the high-cost abatement area (“H”) and the low-cost abatement area (“L”), with vastly different marginal costs (MC) of abatement. The total costs of abatement, the respective shaded areas in this graph, will be vastly different, too:

Now consider the idealized linked market. Total abatement (ΣX) will remain the same. The difference? Prices equilibrate across markets, with PL now equal to PH, lowering the total cost of achieving the same tons of carbon dioxide-equivalent (CO2e) abated.

Abatement costs clearly matter. The lower the costs of achieving the same goal, the better. All else equal, the two jurisdictions can now afford to abate more at the same cost.

There, too, the simple textbook case can be instructive. Linking implies sending money from country H to country L to pay for the cheaper abatement. This raises important questions of baselines, accounting, and transparency. Moreover, lower abatement costs are not the only objective of climate policies. Direct support for the deployment of new, cleaner technologies often tops the list. Given the political economy of reducing greenhouse-gas emissions in the first place, there are many competing domestic objectives and indeed real tradeoffs that need attention.

The big question then is what linkage does to the overall level of policy ambition. Lower costs imply the potential for more ambitious policies. That is clearly good but the devil is in the details. It is important to assure that coordination and collaboration among different jurisdictions really do raise the level of ambition, as the Paris Declaration pledges.

It is also clear that climate policy overall ought to have a balance of bottom-up and top-down policies. Linkage is one potentially important element in that equation. The ultimate measure, however, is tons of greenhouse gases abated from the atmosphere.

In the face of havoc wrought by recent storms and hurricanes, Moody’s Investors Services, Inc. has declared that state and local bondholders must account for climate change or face downgrades. It is the first of the three major credit rating agencies to incorporate climate change risks into its ratings assessment, a move that may incentivize policymakers to make smarter, long-term investments in resilience efforts like stormwater systems or flood management programs.

Bond rating agencies like Moody’s help investors determine the risk of companies and governments defaulting on repayments. Revenue, debt levels, and financial management are all common measures of creditworthiness.

States at high risk–mainly on the coast–including Texas, Florida, Georgia and Mississippi, will have to account for how they are preparing for the adverse effects of climate change, including the effects of storms and floods, which are predicted to become more frequent and intense as temperatures climb.

In its report to its clients, Moody’s outlined parameters that it will use to assess the “exposure and overall susceptibility of U.S. states to the physical effects of climate change.” Some of these parameters include reviewing an area’s economic, institutional, fiscal strengths, and susceptibility to event risk – all of which will influence the borrower’s ability to repay debt. Coastal risks, like rising sea levels and flooding, and an increase in the frequency of extreme weather events, like tornadoes, wildfires, and storms, are just a few of the indicators that will be incorporated into the rating.

This wasn’t always the case. Take New Jersey’s Ocean County, for example. In 2012, Hurricane Sandy devastated Seaside Heights, destroying local businesses and oceanfront properties. Yet, last summer, Ocean County sold $31 million in bonds maturing over 20 years – bonds which received a perfect triple-A rating from both Moody’s and S&P Global Ratings. In 2016, major bond companies issued triple-A ratings for long-term bonds to Hilton Head and Virginia Beach, despite the U.S. Navy’s warnings that the latter faced severe threats from climate change. A recent World Bank study calculated future urban losses that many coastal cities may face because of climate change; Miami, New York, New Orleans, and Boston ranked highest in overall risk. In March 2016, Moody’s and S&P gave top ratings to bonds issued by Boston of $150 million maturing over 20 years, evidently not accounting for any associated climate risks.

The hope: in facing the threat of a rating downgrade and more expensive debt, local governments should move to implement major adaptation and resilience projects as a way to entice investors, and of course, to plan for the effects of climate change.

The California Air Resources Board’s November 6 release of 2016 greenhouse gas (GHG) emissions data from the state’s largest electricity generators and importers, fuel suppliers, and industrial facilities shows that emissions have decreased even more than anticipated. California’s emissions trends are showing what is possible with strong climate policies in place and provide hope even as new analysis projects that global emissions will increase by 2% in 2017 after a three-year plateau.

California’s emissions kept falling in 2016

The 2016 emissions report, an annual requirement under California’s regulation for the Mandatory Reporting of Greenhouse Gas Emissions (MRR), shows that emissions covered by the state’s cap-and-trade program are shrinking, and doing so at a faster pace than in prior years. Covered emissions have dropped each year that cap and trade has been in place, amounting to 31 million metric tons of carbon dioxide-equivalent (MMt CO2e) over the whole period, or 8.8% reduction relative to 2012. The drop between 2015 and 2016 accounts for over half of these cumulative reductions (16 MMt CO2e; 4.8% reduction relative to 2015). The electricity sector is responsible for the bulk of this drop: electricity importers reduced emissions about 10 MMt CO2e while in-state electricity generation facilities reduced emissions by about 7 MMt CO2e.

Some sectors’ emissions grew in 2016. Just as with global transportation emissions, California’s transportation emissions have steadily crept up in recent years, and the MRR report suggests this trend is continuing. Transportation fuel suppliers, which account for the largest share of total emissions, reported a 1.8 MMt CO2e increase in emissions covered by cap and trade since 2015. Cement plants and hydrogen plants also experienced small increases in covered emissions. One of the benefits of cap and trade, however, is that if the clean transition is occurring more slowly in one sector, other sectors will be required to reduce further to keep emissions below the cap while the whole economy catches up.

Emissions that are not covered by the cap-and-trade program dropped, from 92 MMt CO2e in 2015 to 87 MMt CO2e in 2016. While small, this represents the largest reduction in non-covered emissions since 2012 and is mostly driven by suppliers of natural gas/NGL/LPG and electricity importers. Net non-covered and covered emissions reductions resulted in a 20.5 MMt CO2e drop in total emissions from these sectors.

These results are a welcome reminder that the cap-and-trade program is working in concert with other policies to accomplish the primary objective of reducing emissions.

The California climate policies are accomplishing their emissions reductions goals

The 2016 MRR data indicate impactful reductions in GHG emissions and progress toward reaching the state’s target emissions reductions by 2020. The 2016 emissions drop is a consequence of several factors: a CARB analysis of the year’s electricity generation points to increased renewable capacity, decreased imports of electricity from coal-fired power plants, and increased in-state hydroelectric power production. To put it in perspective, the 20.5 MMt CO2e emissions reductions is equivalent to offsetting the energy use of about 2.2 million homes, or 16% of California’s households.

Emissions below the cap are a climate win, not a concern

Total covered emissions in 2016 were about 324 MMt CO2e, well below California’s 2016 cap of roughly 382 MMt. Some observers of the cap-and-trade program worry that an “oversupply” of credits will result in reduced revenue for the state and lesser profits for traders on the secondary market. This concern was especially pronounced when secondary market prices dipped below the price floor in 2016 and 2017.

Importantly, oversupply of allowances is not a bad thing for the climate. As Frank Wolak, an energy economist at Stanford, points out, oversupply may be a sign of an innovative economy in which pollution reductions are easier to achieve than anticipated. Furthermore, having emissions below the cap represents earlier than anticipated reductions which is a win for the atmosphere. Warming is caused by the cumulative emissions that are present in the atmosphere so earlier reductions mean gases are not present in the atmosphere for at least the period over which emissions are delayed.

While market stability is a valid concern, the design of the program has built-in features to prevent market disruptions. Furthermore, the California legislature’s recent two-thirds majority vote to extend the cap-and-trade program through 2030 provides long-term regulatory certainty. Both the May and August auctions were completely sold out suggesting that the extension has succeeded in stabilizing demand.

These results are a welcome reminder that the cap-and-trade program is working in concert with other policies to accomplish the primary objective of reducing emissions, and that we’re doing it cheaply is an added bonus. Early reductions at a low cost can lead to sustained or even improved ambition as California implements its world-leading climate targets.

As California closes its fifth year of cap and trade, it should be with a sense of accomplishment and optimism for the future of the state’s emissions.

More than 200 world leaders met over the last few days at the United Nations’ Annual Climate Change Conference in Bonn to discuss how to fill in the details of individual countries’ pledges of the Paris agreement. And while the United States has clearly ceded its leadership role to China, Germany, France, Canada and others, there are clear signs that adopting an ambitious climate policy is smart for long-term economic prosperity.

Economists across the political spectrum agree that the market alone will not solve climate change, because carbon pollution is still largely unpriced. From an ideal point of view, the optimal climate policy would be a global carbon price. If an appropriate and sufficiently robust global carbon price existed, with clear declining limits on pollution, no other climate policy would be needed.

Unfortunately, such a carbon policy does not currently exist. So, in the absence of such a global pricing regime, what kind of climate policy is cost-effective? Each individual climate policy can be judged on its merits, and most typically show large economic gains, as the benefits of avoiding climate change far outweigh the costs.

Ambitious climate policy passes a benefit-cost test by using the Social Cost of Carbon

To understand the benefit of climate policy, we first need a sense on the magnitude of the climate damages that can be avoided. The current economic consensus view quantifies the social cost of carbon – that is the damage from emitting one ton of CO2 – at $42 per metric ton of CO2 emissions in 2007 U.S. Dollars based on work by the U.S. Government’s Interagency Working Group on Social Cost of Greenhouse Gases.

But what about the cost of climate policy? For many, the potential cost of enacting ambitious climate policy has become a powerful argument against taking any sort of action. So how can we tell if enacting climate policy is cost-effective? A first pass is to subject individual climate policy proposals to benefit-cost analyses that weigh the cost of the specific policy against the avoided climate damages using the social cost of carbon. For example, if the climate mitigation component of a renewable energy proposal costs less than the social cost of carbon, then the policy is good economics.

On the flip side, failing to pass a benefit-cost test does not necessarily imply that a policy is not cost-effective. The social cost of carbon still only captures some of the damages, and future revisions will in all likelihood correct it upwards. Additionally, a policy might lead to important co-benefits beyond climate policy such as reductions in criteria pollutants that have negative effects on human health and the environment.

The Clean Power Plan can serve as a good example to illustrate the argument. Using benefit-cost analysis based on the social cost of carbon, the EPA determined that the Clean Power Plan is a worthwhile investment, with net gains totaling billions of dollars. This is the case even when ignoring any non-climate co-benefits, and when using the lower consensus estimate for the social cost of carbon. Relying instead on the newly available climate impact estimates adds several billion dollars to the net benefits.

Climate policy can go hand in hand with economic prosperity

Moreover, the evidence suggests that – contrary to what some claim – we can implement climate policy while growing the economy. While there can be small adjustment costs, climate policy also leads to lead to new opportunities and innovation. Patenting in clean technologies, for instance, is as vibrant as in biotech, translating into additional growth benefits for the economy as a whole.

Uncertainty makes acting now even more compelling

While there is uncertainty as to just how much CO2 levels in the atmosphere will rise, we know it will be more than ever before encountered by modern humans. And, we already know the economic impacts will be bad. The devastation from hurricanes Harvey, Irma and Maria—made worse by the impacts of a warming climate—will cost communities, taxpayers and insurance companies billions.

But things could turn out much worse. Theoretically, catastrophic climate damages could be so highas to dominate any benefit-cost analysis. This as of yet unpriced uncertainty is a compelling reason to act, not to wait. How to quantify uncertainty with precision is still at the frontier of climate economics. A recent working paper at the NBER calibrates a climate-economy model to financial risk attitudes. The authors find that taking the uncertainty in climate impacts seriously will increase the social cost of carbon even more.

The economic case for ambitious climate action is clear. With the right policies, the benefits of avoiding climate change far outweigh the costs. And in the absence of a price on carbon, the only question is: what are the right climate policy instruments? As EDF has long argued, political debates in climate policy must not be over the if, but the how.

At a recent EDF board meeting, Geoffrey Heal talked about the economic values that ecosystem services provide for our economic well-being. His presentation included a number of case studies, including the New York City Department of Environmental Protection’s financial support for farmers in the Catskills to farm in ways that protect the city’s water quality. The key to the business model: farmers benefit by getting financial support from the City of New York, and the city avoids having to go through a costly filtration system to physically remove impurities or contaminants in a series of filters. The city water supply does undergo UV decontamination.

Last week, the staff of EDF’s Office of the Chief Economist decided to see for ourselves how this works in practice. We visited with Gibson Durnford, the East of the Hudson Agricultural Coordinator of the Watershed Agricultural Council, based in Yorktown Heights, New York. A non-profit organization led by local farmers, it started in 1993 to lead and administer the program.

Incentives for farmers and the City are aligned

Gibson explained that customers in New York City consume 1 billion gallons of water a day, which is supplied from the West and East Hudson systems. There is one and a half years of water in storage (550 billion gallons).

If farmers did not protect the Delaware and Catskill water sheds, the City would have to make a an estimated capital investment of $8-10 billion in water filtration plants and spend an additional $100 million annually to operate them. Phosphate is a particular problem, and the city would also have to deal with sediment running off the farms into the water supply system.

For farmers, payments for eco-services compensate and empower private landowners to be surface-water stewards of New York City’s drinking water. Whole farm management plans are agreed with farmers, incorporating best management practices that both support sustainable farming and protect water quality; concentrated manure sources like slurry pits or storage piles are a greater concern than waste in the fields. If fields are well-vegetated with grass, the plants will take up nutrients; the vegetation slows water flow and also makes the soil more porous and increases absorption.

Farmers are provided with investment funds for purposes which include drainage, roading, manure pads, and sward management; conservation easements are purchased (a percentage of market value) which simultaneously lets the farmer retain ownership of the land, releases capital for the owner while ensuring that the land remains available for farming and forestry; the forest program helps farmers with erosion control, sustainable harvesting, and planting on the banks of tributaries.

Conservation in action at an Alpaca farm We visited Leda Bloomberg and Steve Cole’s Faraway Farm, where they raise Alpaca sheep for their wool. The Watershed Agricultural Council supported the installation of a manure pad, and of a rocky channel along the roadway had drains it to collect the water running off the field and divert it away for infiltration into the soil. Leda and Steve indicated that they had benefited greatly from the advice and support of the Watershed Council. The council is “on the side of the farmers” and is proactive in finding new and better ways to conserve and better their well-being.

The economist Ronald Coase won the Nobel Prize, in part for theorizing (without evidence) that those who pollute could negotiate a solution with those who would benefit from pollution reduction. We were honored and delighted to see his theory being acted upon to such great positive effect for both farmers upstate and the water consumers in New York City. As we left, we had only one question: Doesn’t such a great idea deserve to be replicated?